Numerical analysis of integrated acoustooptic tunable filters with weighted coupling

A numerical approach based on the finite element method (FEM) and the beam propagation method (BPM) is newly formulated for design and modeling of integrated acoustooptic tunable filters (AOTF´s) with weighted coupling on a piezoelectric substrate. First, acoustical field profiles in the substrate region and on the substrate surface are separately calculated with FEM and BPM, respectively. These two-dimensional (2-D) profiles are used for constructing three-dimensional (3-D) strain and electric field profiles. Then, from the strains and electric fields the refractive index changes due to acoustooptic (AO) and electrooptic (EO) effects are derived. Finally, by analyzing modified optical waveguides with AO8- and EO-induced changes in refractive indexes using again BPM, optical filter characteristics of AOTF´s can be evaluated. Numerical examples are shown for AOTF´s with a tapered acoustical directional coupler on a LiNbO₃ substrate